The present invention relates to focused ion/electron beam technology, and more particularly to a charged particle source capable of emitting a high repetition-rate pulsed beam up to the GHz band stably, without causing variations in energy of emitted, charged particles.
A pulsed, focused beam has not yet been used, but can be produced by the prior art. As is evident from JP-B No. 52-35839 (published on Sept. 12, 1977), an emission current can be varied in such a manner that a control electrode is disposed in the neighborhood of a tip electrode and a voltage applied to the control electrode is varied. In more detail, the above publication discloses that the emission current can be stabilized by feeding a monitor current signal back to the voltage applied to the control electrode. Accordingly, it is possible to produce a pulsed beam by applying an A.C. voltage (for example, a high frequency voltage) to the control electrode. In this case, however, an A.C. electric field (that is, a high frequency electric field) which is generated on the basis of the high frequency voltage applied to the control electrode, is superposed on an acceleration electric field. When ions, which are larger in mass and hence lower in traveling speed than electrons, are generated and accelerated, the electric field intensity of an acceleration region varies while the ions travel through the acceleration region. Accordingly, the kinetic energy of an accelerated ion depends upon the phase of high frequency voltage at the time when the ion is generated. This causes the energy dispersion of an ion beam. This energy dispersion increases as the repetition rate of the pulsed beam is larger. Furthermore, in a case where a pulsed beam having a repetition rate in the GHz band is generated, it is necessary to use microwave circuit technology, and it is difficult to apply such technology to a conventional source for emitting a focused, charged-particle beam.
Further, JP-A No. 56-1120582 (laid open on Sept. 4, 1981) discloses a high intensity ion source in which a tip electrode is covered with a liquid metal and the liquid metal is subjected to an electric field for emission of ions.